What's Hiding in Your Hotel Room?

From the swankiest five-star resorts to more modest accommodations, hotels offer refuge, a place to unwind and lay your head for a good night's sleep. But, beware: There could be some unwanted guests resting -- or nesting -- with you.

While staying a Manhattan hotel, two Swiss tourists claim bedbugs left them covered with itchy red welts from head to toe.

Jan Chung says she had a similar experience. She flipped over the blanket in her hotel room and discovered bedbugs.

"I don't exactly remember how many, but I started killing them," Chung said. "Oh, it was so disgusting!"

But what about the things lurking that you can't see or feel? ABC News Primetime went to 20 well-known hotels in New York, Miami, Houston and Los Angeles to find out just how clean the rooms really are. Armed with a black light, they searched for evidence.

What the Black Light Revealed

Inside a $300-a-night room at one of New York's finest hotels, there was dried semen on the bedspread and urine stains on the bedroom walls.

At a Miami hotel, part of a well-recognized chain, the black light revealed an unusual pattern in the carpeting in the bedroom. That pattern turned out to be trails of urine.

"Either somebody was doing something they shouldn't have," said Dr. Mark Callahan, a physician at New York Presbyterian Hospital, "or alternatively, they may have had an animal in there."

At another four-star resort, the black light illuminated traces of urine on the walls, the bedspread, chairs, a bathroom vanity stool and on the carpet right where people step into bed.

Regardless of cost -- from a one-star hotel room priced at $55 a night to a five-star room hotel room renting for $400 a night -- lab results showed traces of urine or semen in every room Primetime tested.

"There's a lot going on behind those doors," Callahan said. "And the reality is that the hotels are not going to be wiping down the walls and those surfaces."

While cleaning crews may dust, vacuum and disinfect daily, most hotels say they do deep cleaning only four times a year, on average -- unless stains are visible. But most unsuspecting hotel guests aren't prepared for the surprises Primetime found, like urine on a hotel Bible.

Tips to Stay Healthy in Hotels

So now you're grossed out, but should you actually worry? Experts say the risk of getting sick from hotel germs is relatively low. Still, if you want to reduce you risk even further, here are some suggestions:

Remove the hotel bedspread. That's typically the most germ-laden thing in the whole room.

Travel with sanitizing wipes. Wipe things that people touch a lot, such as the phone and the remote.

Wash your hands. The main way you can get sick is by getting lots of germs on your hands, then putting your hands in your mouth. So remember what your mother told you, and wash your hands early and often.

Look for rust-colored stains on sheets and bedspreads. It can be a sign that bedbugs are present.